The present invention relates to a rotatable boring bar for machining borehole surfaces which are arranged axially spaced from each other, and more particularly relates to the cutting devices on the bar and to the means actuating and the means guiding the cutting devices.
In producing boreholes of the above mentioned type and, in particular, crank-shaft and cam-shaft bearing holes, tools having a cutter are used. The tool is first introduced into the first bearing hole in order to machine its surface. In this connection, in-feed is correspondingly slow. Upon completion of the first bearing hole, the tool is moved forward in an accelerated manner in order to machine the next bearing hole. It has been found that machining time is relatively lengthy due to successive machining of bearing holes which are arranged in a row.
Boring bars have therefore been employed which have several cutters distributed along the length direction of the rotatable boring bar. The cutters are arranged on an imaginary line which extends parallel to the central axis of the boring bar. In order to introduce the boring bar into the workpiece to be machined, for instance an engine block, the workpiece is lifted. When all cutters are arranged directly in front of the bearing hole surface to be machined, the engine block is lowered again. After the borehole surfaces have been machined, the engine block must be lifted again so that the boring bar can be moved out of the workpiece without injuring the surface of the borehole. This manner of machining is relatively expensive. Furthermore, the displacement of the engine block causes inaccuracies upon machining of the borehole surfaces.